Fix the missing lifetime specifier error by adding a lifetime parameter like 'a to both the input reference and the return type in your function signature.
Add an explicit lifetime parameter to the function signature to tell the compiler how long the returned reference is valid relative to the input.
fn first_word(s: &str) -> &str {
// ... implementation
}
// Fix: Add 'a to both input and output
fn first_word<'a>(s: &'a str) -> &'a str {
// ... implementation
}
The 'a lifetime parameter links the input s and the return value, ensuring the returned reference never outlives the string slice it points to.
The "missing lifetime specifier" error happens when Rust cannot determine how long a reference will stay valid. You fix it by adding a lifetime label, like 'a, to tell the compiler that the data you are returning must live at least as long as the data you received. Think of it like a lease agreement: you are promising the user that the data you hand them won't expire before the original data source does.